This application claims the priority of European Patent Application No. 01 116 015.7 filed Jul. 2, 2001, the disclosure of which is being incorporated herein by reference.
The invention relates to an optoelectronic device for detecting labels with defined contrast patterns. In particular, the optoelectronic device can be embodied as a barcode reader.
Optoelectronic devices of this type comprise a transmitter for emitting light rays, a receiver for received light rays, as well as a deflection unit with a motor-driven polygonal mirror wheel. The transmitted light rays and the received light rays are guided over the polygonal mirror wheel. As a result of the rotational movement of the polygonal mirror wheel, the transmitted light rays are deflected such that they periodically sweep across an area where the labels are located.
The transmitted light rays are guided across the labels in order to scan the patterns thereon. The received light rays, which are reflected back by the labels, are amplitude modulated in accordance with the label contrast pattern. The correspondingly modulated receiving light signals at the receiver output are evaluated in an evaluation unit for detecting the labels.
The polygonal mirror wheel is motor-driven, so that the polygonal mirror wheel performs a rotational movement with a predetermined speed. Commercially available motors with an integrated motor control are normally used for this. The motor is additionally provided with a shaft. A mechanical holding fixture is attached to this shaft and the polygonal mirror wheel is mounted on the top of this fixture. For this, the polygonal mirror wheel preferably is provided with a mounting support for screwing on the holding fixture. The shaft itself is inserted into a bearing and is secured there with fastening means. The motor control is connected via cable to the evaluation unit, which is arranged on a separate printed circuit board. The cable end is provided with a contacting plug that is plugged into a corresponding socket on the evaluation unit.
The disadvantage of a deflection unit with this type of design is that it comprises a plurality of electrical and mechanical components. The assembly of these components is time-consuming and thus represents an undesirably high cost factor when producing the optoelectronic device. In addition, the tolerances of the individually produced components lead to problems with the accuracy of the deflection units produced in this way. Finally, deflection units with this type of design have an undesirably large structural size.
It is the object of the invention to develop a deflection unit for an optoelectronic device of the aforementioned type, which has the smallest possible structural size at the lowest possible production cost, and with a smaller number of production parts than known optoelectronic devices.
The features of the optoelectronic device according to the invention are designed to solve this problem. Advantageous embodiments and useful modifications of the invention are described in the claims.
The optoelectronic device according to the invention is used to detect labels with defined contrast patterns and comprises a transmitter for emitting light rays, a receiver for receiving light rays from a label and for generating receiving signals and a deflection unit with a motor-driven polygonal mirror wheel. The transmitted light rays are guided over the polygonal mirror wheel in order to scan the labels and the reflected, received light rays are also guided across the polygonal mirror wheel. The optoelectronic device according to the invention furthermore comprises an evaluation unit for evaluating the receiving signals present at the receiver. The motor for driving the polygonal mirror wheel has a drive shaft and is provided with a magnet, which is embodied as an injection-molded part. The magnet is molded onto the shaft and operates jointly with at least one coil.
One essential advantage of the device according to the invention is that the shaft with molded-on magnet forms an extremely compact structural unit that can be produced inexpensively. In particular, no additional adapters or the like are required to connect the drive shaft to the magnet. As a result, the motor for driving the polygonal mirror wheel can be produced efficiently with a small number of individual parts and with extremely small dimensions.
An additional advantage is that the shape of the magnet can be specified freely due to the injection-molding procedure, which forms the magnet. In particular, the outside contour of the magnet can be designed such that the polygonal mirror wheel is fitted directly onto the magnet and can be secured, for example, by gluing it on.
Separate mechanical means for attaching the polygonal mirror wheel to the magnet are not required according to the invention, which results in a further reduction of the individual parts and thus a further lowering of the assembly and material costs when producing the deflection unit. The size of the deflection unit is additionally reduced further with this type of design.
In one particularly advantageous embodiment of the invention, the motor is mounted directly on a printed circuit board with an integrated evaluation unit. As a result, the motor, which operates jointly with the coil, is thus actuated directly via this evaluation unit. Consequently, a separate motor control, as well as an electrical cable and plug connection between a motor control of this type and the evaluation unit may be dispensed with.
The drive shaft according to the invention rotates inside a bearing. The bearing is positioned inside a tube. In an embodiment of this type, the tube with the bearing for guiding the motor shaft and the coil, which operates jointly with the magnet, rest on the printed circuit board.
According to this embodiment, the motor shaft is inserted with its lower end into a bearing bore that opens up at the tube top. The motor shaft does not need to be secured inside the bearing, which is particularly advantageous as it is possible to dispense with additional means for securing.
As a result of this structure, the shaft can be moved in a longitudinal direction; but this movement is limited by an end stop, formed by a housing ceiling of the optoelectronic device. The housing ceiling is located close to the upper edge of the shaft, provided the shaft is in the desired position. If the shaft with magnet is moved upward inside the bearing bore, for example as a result of impact on the device, the end stop will push the shaft back to its desired position without this hindering the rotational movement of the deflection unit.
A device according to the invention of this type requires only a small number of mechanical and electronic individual components and as a result, can be produced inexpensively.